1. Field of the Invention
The present invention generally relates to a method and apparatus for setting a master node of a ring network, more particularly, to a method and apparatus for setting a master node of a ring network having a RAS (Reliability, Availability, Serviceability) function that adaptively switches interconnection channels during failure.
2. Description of the Related Art
The IP (Internet Protocol) network, performing various kinds of data communication, is basically structured with a mesh topology. It is, however, not always best to employ the mesh topology for a network. For example, for a network for monitoring bidirectional communications between a plurality of stations in a limited area (e.g. road, river), a linear type or a ring type network may be efficiently used. It is to be noted that ring networks having a RAS function include a serial transmission type and a loop back transmission type.
For example, in Japanese Examined Patent Application No.7-52886 and Japanese Laid-Open Patent Application No.2002-171268, the inventor of the present invention proposes a method and apparatus for setting a master node of a linear or a ring network that is able to fully utilize the transmission capacity of a bidirectional transmission channel for efficiently transmitting data, and to simultaneously perform data communications between plural nodes without causing delay in data transmission.
FIGS. 1A and 1B are drawings for describing an exemplary structure of a ring network. For example, in the ring network shown in FIG. 1A, node A, among random nodes, is an end station (master node) and the remaining nodes B through D are intermediary stations (slave nodes), wherein each of the nodes is connected to an adjacent node with a bidirectional transmission channel. The ring network shown in FIG. 1A is, logically, equal to the linear structure shown in FIG. 1B.
In FIGS. 1A and 1B, the node (end station) A operates as left and right end stations. The left and right end stations generate a packet trailer that includes a token packet (including transmission authority information), and data packet storage space. The left end station transmits the packet trailer in the rightward direction of the transmission channel, and the right end station transmits the packet trailer in the leftward direction of the transmission channel (line). In requesting a data packet (information) to be transmitted in the rightward direction, each intermediary station writes information requesting the transmittal of the data packet onto the token packet in the packet trailer heading leftward on the leftward transmission channel, and in requesting a data packet (information) to be transmitted in the leftward direction, each intermediary station writes information requesting the transmittal of the data packet onto the token packet in the packet trailer heading rightward in the rightward transmission channel (line).
Based on the information written onto the token packet in the packet trailer sent from an oppositely situated end station, each of the right and left end stations generates a packet trailer having data packet storage space reserved for the intermediary station that has requested transmittal of the data packet. The intermediary station having requested the transmittal of the data packet (information) stores the data packet in the reserved space in the packet trailer, and transmits the packet trailer containing the data packet to a destination node.
An operation of a conventional ring network, in a case where there is a failure in a line of the network, is described with reference to FIGS. 2A through 2D. As shown in FIG. 2A, when the ring network is in a normal state, node A operates as the end station (master node), and the remaining nodes B through D operate as intermediary stations (slave nodes). When there is a failure between nodes C and D as shown in FIG. 2B, nodes C and D, having the failure therebetween, operate as end stations (See FIG. 2C). After communication is restored, either one of the nodes C or D operates as the end station as shown in FIG. 2D (in this example, node C).
It is to be noted that, conventionally, in handling information for distinguishing transition of the nodes, a part of the bandwidth of both rings is fixedly allocated, and a dedicated band which is logically different from the main signal is used. With the conventional example, the master node moves during operation, and is unable to have a fixed position in the network.
In a network where traffic runs evenly throughout the nodes, the position of the master node causes no decrease in transmission efficiency. However, in a network where reception traffic is concentrated on a particular node, the position of the master node may decrease transmission efficiency.
In a normal operation state of a ring network, packets can be transmitted in both left and right directions. Accordingly, transmission efficiency is greatly affected by the position of the master node which performs arbitration. In a case where reception traffic is concentrated on a particular node, excellent performance can be attained when the particular node is situated furthest from the master node.
The differences in transmission efficiency in relation to the position of the master node are described with reference to FIGS. 3 through 5. Since the ring network is illustrated in a spread-out manner, node #1, which is the master node, is illustrated on both ends of the network.
In the ring network shown in FIG. 3, a once-used band will not be available until terminating at the master node. Normally, communication from one node to another is performed evenly on a substantially same band, and the total of the communications is equal to the bandwidth of the transmission channel.
As shown in FIG. 4, in a case where the reception traffic from nodes #1 through #7, #9 and #10 is concentrated on node #8, all of the bands of the lines in the rightward direction are used while there are still bands available in the leftward direction. Therefore, in a case, for example, where nodes #6 and #7 to node #8 request communication, neither can the nodes #6 and #7 to node #8 perform communication nor can the total amount of communication be increased since all of the bands of the lines in the rightward direction are occupied. This is because the packet trailer is generated and sent by the node #1 (master node), and thus terminates at the node #1. Accordingly, although there are bands remaining in the leftward direction, the bands cannot be used. This occurs most notably when the node to which the reception traffic is concentrated (in this example, node #8) is situated other than a position furthest from the master node (in this example, node #1).
On the other hand, as shown in FIG. 5, in a case where the reception traffic from nodes #1 through #5, and nodes #7 through #10 is concentrated on node #6, the bands of the lines in both left and right directions can be efficiently used when the node to which the reception traffic is concentrated (in this example, node #6) is situated at a position furthest from the master node (in this example, node #1).
The foregoing description of the conventional network shows that {circle around (1)} transmission efficiency significantly differs depending on the position with respect to the master node, {circle around (2)} an excellent transmission performance can be attained when the node to which the reception traffic is concentrated is situated at a position furthest from the master node, {circle around (3)} the master node moves during operation and cannot have a fixed position in the network. Accordingly, in the conventional network where there is a concentration of reception traffic, the network may be subjected to a decrease in transmission efficiency due to the position of the master node.